Ultrasonic devices for determining distances have heretofor tended to be expensive because of the complex circuitry involved. Until recently crystal-generated ultrasonic signals started at very small amplitude and only gradually increased to a peak value, held at the peak value for a time, and then gradually decreased.
On the other hand, electrostatic devices required expensive and complex circuitry. One of the best such devices required four circuit boards, and this complexity also rendered failure more likely.
Recently, advances in piezoelectric technology has made crystal-type transducers less expensive, more rugged, easily cleanable and also able to produce a fast rise time pulse that makes high resolution possible. The present invention makes it possible to provide a simple relatively inexpensive decoding circuit, so that overall the cost per unit including both the transducer and the circuit is less than half of that of the electrostatic transducer-circuit combination. The system of this invention requires only a single circuit board and, having many fewer parts, is less likely to fail. Moreover, if a component should fail, it becomes much easier and quicker to locate the trouble and remedy it.